Photosynthesis

Question 1

Word equation for photosynthesis

Answer 1

Carbon dioxide + water –> Glucose + oxygen

Question 2

Chemical equation for photosynthesis

Answer 2

6CO2 + 6H2O –> C6H12O6 + 6O2

Question 3

Pondweed photosynthesis experiment using CORMS

Answer 3

Change : Distance between lamp and beaker containing pondweed.
Organism: Elodea (pondweed)
Repeat: 10 x
Measure: Number of 02 bubbles produced in a minute at each distance. To improve experiment measure volume of 02 bubbles.
Same: Length of elodea, temperature, species of plant, type of light bulb, CO2 concentration

Question 4

Control variables in pondweed experiment

Answer 4

Length of elodea used, temperature of beaker, species of plant, type of light bulb, CO2 concentration

Question 5

Independent variable in pondweed experiment

Answer 5

Intensity of light/ distance between lamp and pondweed.

Question 6

Dependant variable of pondweed experiment

Answer 6

Number of oxygen bubbles produced by pondweed in a minute or volume of oxygen bubbles produced by pondweed in a minute

Question 7

Improvements to pondweed experiment

Answer 7

Keeping temperature controlled so rate of photosynthesis isn’t affected: Put the elodea in a boiling tube of water which is then placed in a beaker with a thermometer, to act as a water bath.
Accurate measurement of O2: Collect the gas (oxygen) produced in an inverted measuring cylinder to measure the volume of oxygen produced per time. Or use a gas syringe.
CO2 concentration: Add a fixed mass of sodium bicarbonate to water to provide a higher, constant concentration of CO2.

Question 8

Steps for testing a leaf for starch.

Answer 8

Destarch the leaf for 24 hours in the dark before starting the experiment.
Place leaf in boiling water for 1 min.
Turn off the bunsen burner and transfer the leaf into a test tube containing ethanol and then place the test tube in hot water.
Place the leaf in hot water to soften it.
Spread the leaf out on a white tile and cover it with Iodine solution.

Question 9

Why is the leaf de-starched in the experiment?

Answer 9

So that the leaf is free from starch at the start of the experiment. Ensures any starch present in the leaves is used up and will no affect the results of the experiment.

Question 10

How does placing the leaf in the dark destarch it?

Answer 10

Without any sunlight, photosynthesis doesn’t take place in the leaf. Photosynthesis produces glucose which is stored as starch in the leaf. Without photosynthesis, no glucose is produced and no starch is stored. The starch stores in the leaf are converted to glucose for respiration, to produced energy for the plant. The starch stores are used up.

Question 11

Why is the leaf placed in boiling water at the start of the experiment?

Answer 11

To kill the tissue and break down the cell walls.

Question 12

Why is the leaf boiled in ethanol?

Answer 12

To dissolve the chlorophyll so colour change can be seen more clearly.

Question 13

Why is the leaf placed back in hot water/ rinsed with water?

Answer 13

To soften the leaf/ to allow Iodine to penetrate the leaf.

Question 14

What colour does Iodine turn in presence of starch?

Answer 14

Yellow –> blue/black

Question 15

How would you change the experiment if you wanted to show that a leaf needed light for photosynthesis?

Answer 15

Cover part of the leaf so it isn’t exposed to sunlight. Only the part of the leaf exposed to sunlight will produce starch and turn blue/black

Question 16

How would you change the experiment if you wanted to show that chlorophyll is required for photosynthesis?

Answer 16

Use a variegated leaf. The white parts of leaf lack chlorophyll. Only the green parts of the leaf (containing chlorophyll) will produce starch. Green parts of leaf contain the green pigment chlorophyll which is used in photosynthesis.

Question 17

How would you change the experiment if you wanted to show that carbon dioxide is needed for photosynthesis?

Answer 17

One leaf of a plant is enclosed in a conical flask (or
plastic bag) containing soda lime to absorb the carbon dioxide and this leaf is compared
to another enclosed in a flask but without the soda lime. Only the leaf that had access to
carbon dioxide produces starch.

Question 18

Explain why the ‘Testing a leaf for starch’ experiment shows what is needed for photosynthesis.

Answer 18

Photosynthesis produces glucose, which is stored in the leaves as starch. When a leaf has photosynthesised, starch will be present.

Question 19

Safety precautions for ‘testing a leaf for starch’ experiment.

Answer 19

Ethanol is flammable so turn off the bunsen burner when boiling the leaf in ethanol. Safest way to heat ethanol is in an electric water bath.
Iodine is an irritant to the eyes so wear goggles.

Question 20

Describe how energy for photosynthesis reaction is gained by plants.

Answer 20

Light is absorbed by chloroplasts/ chlorophyll

Question 21

Limiting factors of photosynthesis

Answer 21

Carbon dioxide, temperature and light intensity

Question 22

Describe and explain the waxy cuticle

Answer 22

Protective layer, prevents water from evaporating

Question 23

Describe and explain the upper epidermis

Answer 23

Thin and transparent to allow light to penetrate through to the palisade mesophyll layer

Question 24

Describe and explain the palisade mesophyll

Answer 24

Long, thin cells tightly packed with lots of chloroplasts to absorb more light, maximising photosynthesis

Question 25

Describe and explain the spongy mesophyll

Answer 25

Contains air spaces that increase surface area to volume ratio for the diffusion of gases

Question 26

Describe the lower epidermis

Answer 26

Contains guard cells and stomata

Question 27

Describe and explain the guard cell

Answer 27

Opens and closes the stomata to allow CO2 to diffuse in and oxygen to diffuse out

Question 28

Describe and explain the stomata

Answer 28

Where gas exchange takes place. Evaporation of water also takes place here.

Question 29

Describe and explain the vascular bundle

Answer 29

Contains xylem and phloem to transport substances to and from the leaf

Question 30

Describe and explain the xylem in the leaf

Answer 30

Transports water into leaf for mesophyll cells to use in photosynthesis and for transpiration from stomata

Question 31

Adaptations of root hair cell

Answer 31

High surface area for maximum water and mineral absorption
Lots of mitochondria so lots of energy produced for active transport of minerals
No chloroplasts, no photosynthesis

Question 32

Why do stomata open in the light?

Answer 32

In light, guard cells photosynthesise, sugar concentration increases (glucose produced) so water potential decreases. Water moves into the guard cells by osmosis so they become turgid. Because of the inflexible inner cell wall the guard cells change shape, opening the stomata.

Question 33

Why do stomata close in the dark?

Answer 33

Photosynthesis doesn’t occur in the dark. Sugar concentration falls (due to respiration), water potential increases and water moves out of the guard cells. This causes the guard cells to become flaccid and the stomata close.